There’s no such thing as a brontosaurus – the half- life of knowledge

While watching an episode from the most recent K series I was shocked to discover that 60% of facts from series A, which was first broadcast in 2003, were wrong. Some of this will be down to errors by the elves. But the vast majority of these will be due to the fact that knowledge is in constant flux. This instability is reflected in a classic QI question: How many moons does the Earth have? The best current knowledge is that there are now about 18,000 of what NASA calls “mini moons”. However, in Series A it was two and in series B this was revised to either one or five.

This revelation about the transitory nature of knowledge made me want to read The Half-life of Facts, a book by Harvard mathematician, Samuel Arbesman. The book’s subtitle is Why Everything We Know Has an Expiration Date. Arbesman is an expert in scientometrics, or the study of measuring and analyzing science, with his main area of study being how facts are constantly being made and remade. He is particularly interested in those facts that change slowly; he calls them mesofacts. The concept of half-life is usually used to refer to radioactive atoms; it is the time it takes for half of a certain substance to decay. Arbesman applies this to scientific knowledge, describing the amount of time that it takes for facts to be proven wrong. He did not invent this concept. Fritz Machlup is the man said to have first referred to the half-life of knowledge.

In 1965 Derek J Solla, a pioneer in the field of scientometrics, found that scientific knowledge is growing at a rate of 4.7 percent annually. Using a simple rule of thumb – dividing 72 by this number – we can learn that at this rate scientific knowledge would double every 15 years or so. This has very practical implications for scientific knowledge. Studies show that the “half-life” of a paper in a physics journal is 10 years. By this we mean the time it takes to lose half its influence. This impact is measured in terms of how often it gets cited, and can be measured with some precision.

Some fields are well aware of this phenomenon. Medical students are taught that everything they learn is going to be obsolete soon after they graduate. There is even a website called www.uptodate.com that constantly updates medical textbooks. I think we should, like medicine, embrace this change. We need to do away with the idea that we can definitively learn a subject. Rather than learning facts and yet more facts, we need to be able to learn how to adapt to changing facts. I do think there is some value to having a basic notion of the facts, but it also true that this can also be outsourced to the cloud.